Many ERP studies have demonstrated that the more deviant a rare stimulus is from the background (i.e., the more easily it can be discriminated), the larger the P3 amplitude (for review, see Regan 1989). This effect was examined in a visual oddball task using line stimuli (Porjesz et al. 1987). P3 components were obtained in response to two target lines—one that was easy to discriminate (90 degrees from a vertical nontarget line), and one that was more difficult to discriminate (only 3 degrees from the vertical nontarget).
